1. Field of the Invention
The present invention relates to an image forming apparatus of an electronic photography type such as a copying machine and a laser printer, and more particularly to the image forming apparatus which is capable of automatically deserting developing powder stored in a developing bath.
2. Description of the Related Art
The inventors of the present application know a mechanism for recovering developing powder. This known recovery mechanism includes a screw for carrying the developing powder into a developing bath. The screw operates to carry the degraded developing powder to a recovery vessel.
The inventors of the present application know another mechanism for recovering degraded developing powder. This known recovery mechanism includes a tabular discharging shutter provided on the bottom of a developing bath. By pulling the discharging shutter out of the developing bath, the degraded developing powder is allowed to be discharged.
The former known mechanism has the following disadvantages, because it provides the carrying screw inside of the developing bath.
(1) In a case that the screw is stopped in doing a copying operation and is started in discharging the developing powder, the stationary developing powder appears near the screw. The pool of the stationary powder makes the density of the developing powder in the bath shifted, that is, cannot offer a uniform density on the overall copied paper.
(2) In a case that the screw is driven in doing a copying operation and deserting the developing powder, the screw operates to shift the developing powder toward a deserting side of the developing bath. This results in disabling to output the developing powder on a magnet roller and varying the overall density of the developing powder.
The latter known mechanism has the following disadvantage. That is, this mechanism is constructed to exchange the developing powder by opening and shutting the shutter on the bottom of the developing bath. In the space around the screw and a pipe from the screw to the vessel, the developing powder is jammed. Hence, it is difficult to smoothly exchange the developing powder at the next time.
Further, the inventors of the present application know that a toner density sensor may be added to the mechanism. The toner density sensor serves to sense the developing powder and sends a sensing signal. Based on the sensing signal, it is determined whether or not the exchange of the toner is terminated. In a case that, however, the developing powder is left at the bottom of the developing bath, the new developing powder is mingled into the left developing powder, resulting in lowering the quality of the image.
As another disadvantage of the latter known mechanism, when the developing powder is dropped into the recovery vessel by opening the shutter, the powder may be splashed here and there. The user may soil his or her hands with the splashed powder.